In order to ensure that a tread performs optimally on all types of ground (dry or wet), it is known to provide this tread with a tread pattern formed of a plurality of tread pattern elements defined by cutouts (adopting the form either of grooves or of incisions), these cutouts opening onto the running surface of the tread when new. The function of these cutouts is to create ridges for cutting through the film of liquid which may be present on the roadway and to serve as passages for the flow of the same liquid in order to improve the safety of a vehicle fitted with such tires on ground covered in liquid.
However, the presence of deep cutouts allowing the technical effects mentioned above to be benefited from for the entire service life of the tread (corresponding generally to the wear limit acceptable for this tread) results in a significant reduction in the overall rigidity of the tread (crushing rigidity and shearing rigidity in a direction parallel to the contact with the ground). To lessen the effect of this reduction in rigidity, it has been proposed, for example in the patent application published under number WO98/54009, to form on the running surface when new grooves of reduced depth, that is to say not involving the entire thickness of the tread and, by way of supplement, channels situated entirely beneath the running surface. These channels do not open onto the running surface when new and are provided to form new grooves after sufficient partial wear of the tread. The grooves opening onto the running surface when new are designed to disappear after wear approaching or slightly greater than the wear necessary for the formation of new grooves by the channels.
The tread patterns produced according to this teaching result in a significant improvement; however, under certain conditions irregular wear may develop at the edges (or ridges) of the tread pattern elements newly created by the new grooves formed at the moment when the channels reach the running surface. Irregular wear means wear which develops more over certain regions of the tread and which does not develop homogeneously within the thickness of the tread; this wear may necessitate premature withdrawal of the tire provided with such a tread.
EP 1125709 describes a tread band comprising incisions having a geometry circular produced by molding thanks to a device having a part mobile in rotation.
It became clear that there was a need for an improvement in tread patterns for heavy vehicle tires which, while achieving good performance levels on various types of ground, allowed maintenance of considerable rigidity and prevention of the appearance and development of irregular wear.